Mehrdad Abolbashari

Active illumination single-pixel camera based on compressive sensing

We present an optical imaging system based on compressive sensing (CS) along with its principal mathematical aspects. Although CS is undergoing significant advances and empowering many discussions and applications throughout various fields, this article focuses on the analysis of a single-pixel camera. This work was the core for the development of a single-pixel camera approach based on active illumination. Therefore, the active illumination concept is described along with the experimental results, which were very encouraging toward the development of compressive-sensing-based cameras for various applications, such as pixel-level programmable gain imaging.

High-resolution hyperspectral single-pixel imaging system based on compressive sensing

For the first time, a high-resolution hyperspectral single-pixel imaging system based on compressive sensing is presented and demonstrated. The system integrates a digital micro-mirror device array to optically compress the image to be acquired and an optical spectrum analyzer to enable high spectral resolution. The systems ability to successfully reconstruct images with 10 pm spectral resolution is proven.

High dynamic range compressive imaging: a programmable imaging system

Some scenes and objects have a wide range of brightness that cannot be captured with a conventional camera. This limitation, which degrades the dynamic range of an imaged scene or object, is addressed by use of high dynamic range (HDR) imaging techniques. With HDR ima- ging techniques, images of a very broad range of intensity can be obtained with conventional cameras. Another limitation of conventional cameras is the range of wavelength that they can capture. Outside the visible wave- lengths, the responsivity of conventional cameras drops; therefore, a con- ventional camera cannot capture images in nonvisible wavelengths. Compressive imaging is a solution for this problem. Compressive imaging reduces the number of pixels of a camera to one, so a camera can be replaced by a detector with one pixel. The range of wavelengths to which such detectors are responsive is much wider than that of a conven- tional camera. A combination of HDR imaging and compressive imaging is introduced and is benefitted from the advantages of both techniques. An algorithm that combines these two techniques is proposed, and results are presented.

Image continuity at different levels of zoom for fringe patterns

Fringe patterns are raw output data from many measurement systems including laser interferometers and moiré systems. For instruments with a range of zoom levels to measure the object at different scales, a technique (algorithm) is needed to combine and/or compare data to obtain information at different levels of details. A technique to keep the continuity of output images both at different levels of zoom and within the same level of zoom is developed and demonstrated. Image registration is used to correlate images, find relative zoom values, and obtain shift between images in the lateral plane. Fringe patterns from a moiré system and a laser interferometer are used as images to be stitched and demonstrate the technique. Interferomteric fringes are used to find the required parameters to inter-relate locations and scale of the fringe patterns at different levels of zoom. The calculated parameters are scale and translation in both directions; these parameters make it possible to locate the coordinates of the region that the measurement system is zoomed in on, related to the area with lower magnification and relative locations of images within the same level of zoom. Results show that this technique is capable of finding the scale and shift parameters within the resolution of one pixel and therefore can restore continuity between images at different levels of zoom.

Image continuity at different levels of zoom for Moiré techniques

Moiré technique is a technique used for 2D and 3D imaging and surface characterization. Moiré systems may have a range of zooms to image an object at different levels of details or Moiré images may be combined (or compared) with images from other interferometers. So, it is needed to inter-relate images together in order to keep the continuity of the images at different levels of zoom or images from different types of interferometers. This paper uses image registration techniques to correlate images and find scale and translation between two images. Image registration is widely used in medical imaging and range imaging to relate two different images from a single object or scene. In this work, only interferograms from two successive levels of zooms of a Moiré system are used. Saved interferograms are correlated using one of the affine algorithms which are used in image registration and then relative scale and shift are calculated. Calculation of these parameters makes it possible to locate the position of area that the Moiré system is zoomed in, related to the area with lower zoom level. Simulation results show that this technique is applicable and successful in finding the scale and shift parameters and therefore can keep the continuity between images at different levels of zoom.

A Compressive Hyperspectral Imaging System based on Parallel Processing

A new approach to hyperspectral compressive imaging system based on parallel processing is developed. The architecture of system is based on single-pixel compressive imaging. By parallelizing the recovery algorithm and using multicore CPUs and GPUs, we address high computational requirement.

Biological imaging with high dynamic range using compressive imaging technique

Scenes in real world have dynamic range of radiation that cannot be captured by conventional cameras. High dynamic range imaging is a technique to capture detail images where, in the field of image, intensity variation is extreme. This technique is very useful for biological imaging where the samples have very bright and very dark regions and both parts have useful information. In this article we propose a novel high dynamic range imaging technique based on compressive imaging that uses one single detector instead of camera (array of detectors) to capture an image. Combination of high dynamic range imaging and compressive imaging benefits from imaging with high dynamic range of radiation and advantages of compressive sampling; namely, imaging at regions of optical spectrum where conventional cameras are not readily available and single detectors are available. Additionally, as its name suggests, this technique requires less number of samples (compared to raster scanning). Our experimental results show that high dynamic range compressive imaging system is capable of capturing images with large intensity contrast.

A compressive sensing based transmissive single-pixel camera

Compressive sensing (CS) has recently emerged and is now a subject of increasing research and discussion, undergoing significant advances at an incredible pace. The novel theory of CS provides a fundamentally new approach to data acquisition which overcomes the common wisdom of information theory, specifically that provided by the Shannon-Nyquist sampling theorem. Perhaps surprisingly, it predicts that certain signals or images can be accurately, and sometimes even exactly, recovered from what was previously believed to be highly incomplete measurements (information). As the requirements of many applications nowadays often exceed the capabilities of traditional imaging architectures, there has been an increasing deal of interest in so-called computational imaging (CI). CI systems are hybrid imagers in which computation assumes a central role in the image formation process. Therefore, in the light of CS theory, we present a transmissive single-pixel camera that integrates a liquid crystal display (LCD) as an incoherent random coding device, yielding CS-typical compressed observations, since the beginning of the image acquisition process. This camera has been incorporated into an optical microscope and the obtained results can be exploited towards the development of compressive-sensing-based cameras for pixel-level adaptive gain imaging or fluorescence microscopy.

A combined fiber Bragg grating and interferometric based sensor

A novel combined fiber Bragg grating (FBG) and interferometric based sensor is proposed and demonstrated. The sensor is based on two overlapped Michelson interferometers working at different wavelengths in a Sagnac loop and two FBGs used as wavelength selective mirrors. The advantage of the system is that it combines the benefit of point measurement with FBG and the high sensitivity of long gauge interferometric sensor.

Fractional bispectrum transform: definition and properties

A signal with discrete frequency components has a zero bispectrum if no addition or subtraction of any of the frequencies equals one of the frequency components. The authors introduce the fractional bispectrum (FBS) transform in which for signals with zero bispectrum the FBS could be non-zero. It is shown that FBS has the same property as the bispectrum for signals with a Gaussian probability density function (PDF). The FBS of a zero mean signal with a Gaussian PDF is zero. Therefore, it can be used to significantly reduce the Gaussian noise.